Investigation of buffer charging effects in GaN-based transistors

  • Alexander Pooth

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


GaN based transistors are investigated in this work. GaN devices have already
been introduced for commercial applications for RF and power markets. Due to
excellent performance achieved with GaN devices, predictions for even greater
commercial success have been made. Some major reliability issues though still
exist which prevent the devices from showing their full potential. One such issue
is the current collapse phenomena which can be related to buffer charging effects.
Those buffer charging effects are investigated in this work.
The impact of carbon doping in the buffer on current collapse is tested for
devices grown on Si substrate. The results are interpreted with the help of simulations.
A clear relation between doping and current collapse is seen.
Different current collapse behaviour is observed on otherwise similar samples.
To get better insight characterisation techniques involving illumination are developed and effects otherwise not accessible are detected. The observations have implications for devices operating under light.
Devices grown on SiC substrates are also tested. Strong impact of ohmic
contacts on leakage is observed. Different doping profiles including carbon and
iron are tested. Based on the findings new structures are proposed and simulated which have the potential to prevent detrimental effects.
Date of Award25 Sep 2018
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorMartin H H Kuball (Supervisor)

Cite this